Flight control technology key to lighter, stealthier UAVs

The University of Manchester and BAE Systems are teaming up to test different technologies aimed at improving flight control of small unmanned aerial vehicles (UAVs). The university/industry group completed the first phase of flight trials late last year with a jet-powered UAV called MAGMA. Project officials say that the end result is to deliver to military and commercial users a lighter, stealthier unmanned system.

The collaborators and the project’s goal is simple, says Brian Oldfield, Lead Technologist, Advanced Structures, at BAE Systems in the U.K.: “MAGMA’s goal is to create a small unmanned vehicle, which can be used to mature research into a number of novel technologies by integrating them into the vehicle design and demonstrating them in flight.”

The project is ongoing for BAE Systems and the university; it’s part of a “wider long-term collaboration between in­dus­try, academia, and government to explore and develop innovative flight control technology,” says BAE Systems.

According to documents from BAE Systems, the new aircraft-control concept will remove “conventional need for complex, mechanical moving parts used to move flaps to control the aircraft during flight,” leading the way for the desired UAV design. The recently completed test with the MAGMA UAV (Figure 1) by the university and BAE Systems focused on two flight controls: wing trailing edge circulation control and fluidic thrust vectoring.

Researchers are shooting for lighter, stealthier flight using these two technologies.Oldfield explains, “The wing trailing edge circulation control devices use air blown supersonically out of small slots to control the direction of airflow at the back of the wing (which in turn influences the flow around the entire wing).”

The concept is “based on an aerodynamic effect called the Coand˘a effect, where a jet of air will attach itself to a curved surface,” he adds. “The freestream flow around the outside of the wing is entrained into the deflected air jet and the entire flow around the wing is therefore changed (a similar effect to deflecting a flap or control surface is achieved).”

By controlling the UAV via the wing trailing edge circulation control method, the resulting benefits could mean a lighter system because its conventional flaps would be replaced by fewer moving parts, Oldfield explains. He also points out that it “may be less observable due to the reduce number of gaps and edges,” hinting at the stealthier part of the equation.

The second flight control that underwent testing also uses the Coand˘a effect. The fluidic thrust vectoring control “allows us to change the direction of the engine thrust; giving maneuverability improvements and the like to the trailing edge devices has potential benefits over a mechanical thrust vectoring system with moving parts,” Oldfield says.

The program doesn’t come without its challenges. The biggest one? “The geometry of the flow control devices are key to getting the right performance, which is both a design and manufacturing challenge, and these need to be fed with the air supply from the engine at the required mass flow rates, to provide efficient control of the vehicle in flight.”

On that subject, from an aerodynamic perspective, “this research has made it possible to make these systems work effectively when the blowing jets are supersonic without the effects of supersonic shock waves causing separation of the jet from the curved surface,” he continues.

Researchers achieved the lack of supersonic shock wave through “the use of geometric features that are used to condition the flow [pressures and velocity gradients] in the jet itself,” Oldfield says. “The use of supersonic blowing jets makes the system efficient from the perspective of minimizing the engine bleed air mass flow required and also of minimizing the sizing of pipe work and valves used to distribute the blowing air around the airframe.”

In addition to the MAGMA work with the University of Manchester, BAE Systems has also been collaborating with the NATO Science and Technology Organization (STO) and the University of Arizona to develop technologies that will improve UAV performance.

With the NATO STO project, the ­collaboration “allows us to exchange information with others working in similar fields.” Oldfield explains. “In the case of University of Arizona, they are looking at a flow control technol­ogy called ‘sweeping jets’ which may enable further efficiency improvements or greater control from these types of de­vices on certain wing geometries through their ability to delay flow separation and influence the direction of the natural wing flow.”

BAE Systems points out that if the MAGMA tests are successful “[they] will demonstrate the first-ever use of such circulation control in flight on a gas turbine aircraft and from a single engine.